The present application claims priority from an application filed in Argentina on Oct. 24, 2001, under application number P 01 01 04978.
The present invention generally relates to devices and processes for estrus synchronization in an organism.
Beef Cattle
The productive cycle of a breeding cow can be divided in three periods:
a) Period of dry cow
b) Calving preparatory period
c) Calving and lactation
Every period has specific nutritional requirements and hormonal characteristics. The pregnancy of the animals involves a substantial cost since the requirements of the last month of gestation are higher than those applicable to a non-pregnant animal.
Besides, if calving is taken as Day 0 of the calendar year, the more synchronic the 0 Days of a herd, the better will the fodder supply adjust to the nutritional needs of the herd, thus improving the physiological needs of the cattle and at the same time addressing an economic issue.
Likewise, the post-calving anestrus period can be shortened allowing for the estrus to occur at the end of the puerperium period. In this way, animals can be served and fertilized quicker, improving not only the corporal condition of the herd and the pregnancy but also the health and welfare of calves because of a reduction of the mother""s stress factors.
The advantages and benefits of a planned reproductive management program are known and can be generally stated as, which may or may not be effected in every planned reproductive management program:
1. Allows for planning of calving dates.
2. Improves the rotational grazing and ensures an efficient distribution of fodder to meet the physiological feeding needs of the cattle.
3. Facilitates the design of calving and service plots and optimizes the work of the personnel.
4. Decreases the number of bulls per herd, allowing for the investment in bulls with superior genetics and quality.
5. Improves the work with the calves, allowing for their distribution in homogenous groups.
6. Enhances the sustainability of the estrus system, thus avoiding dependence on natural periods.
7. Allows for a strategic supplementation management of the herd and optimizes supplemental doses.
8. Facilitates compliance with the vaccination program and improves its efficiency.
9. Shortens the service season and allows to produce one calf per cow served per year.
10. Facilitates the use of artificial insemination at a large scale, the application of an improved genetics and the practice of industrial cross-breeding.
11. Allows for a fixed-time artificial insemination process, without estrus detection.
12. Facilitates the control of returns to service.
13. Increases the fertility rate in heifers and allows for the insemination of a high number of animals per day.
14. Facilitates the insemination of animals with deficient estrus onset.
15. Facilitates the insemination of 15-month animals even when their luteus phases are not mature yet.
16. Facilitates the synchronization of receptors for embryo transfer.
17. Gives economic benefits.
Reproductive Efficiency of the Breeding Cattle
The productivity of the breeding cattle depends largely on its reproductive efficiency. The former is measured in terms of kilogram of calf per served cow while the latter is measured in terms of pregnancy rate or percentage. However, the most important parameter to individually evaluate the reproductive efficiency is the interval between calvings that, in economic terms, should not exceed the optimum period of 365 days, that is to say, a calf per cow per year. The main determining factor of the calving interval is the calving-conception interval that, considering a constant pregnancy period of 280 days, should not exceed 80-85 days, in most breeding facilities and most climates.
Some quantitative ratios between these parameters have been already established and the observations show that the pregnancy percentage falls linearly when the calving-estrus interval increases from 60 to 120 days. This calving-first estrus relationship shows that calf kilograms decrease considerably when such interval is extended and the loss amounts to 833 g per day.
Naturally, management decisions and procedures have some influence on the calving-conception interval but the latter is mainly determined by the following three factors:
1. The reestablishment of ovarian cycles after calving.
2. The occurrence of the estrus at the proper time of the cycle
3. The pregnancy rate after the service.
In this ratio, the pregnancy rate increases almost linearly when the estrus fertility increases. The slope depends on the calving-estrus interval, and it increases when this interval shortens.
When the calving-estrus interval is 60 days, a fertility increase, for example by reducing the services from three to two per served cow, results in a 16% increase in pregnancy percentages. The analysis of these quantitative ratios illustrates the impact of these parameters on the productivity of a breeding herd. Therefore, it is worth analyzing the way in which environmental factors influence the calving-conception interval.
Dairy Cattle
The benefits of a planned reproductive management in dairy cattle include the predetermination of the calving date and, therefore, of production; the possibility of facilitating the implementation of artificial insemination by reducing the estrus detection tasks and increasing the overall reproductive efficiency of the breeding operations.
The adoption of estrus cycle handling systems in dairy cows is increasingly important nowadays if we consider the need of streamlining the productive systems by improving production during the life of the animal and reducing the calving-conception intervals since this process results in an increase in the number of productive days of the animals. Given the fact that the grazing production systems of our country have a natural seasonality, cows must be fertilized at predetermined dates.
It has been said that the adoption of a scheduled reproductive management system improves the reproductive efficiency of the herds. Therefore, in various operations suitable parameters may include:
Out of all the abovementioned, the most frequently used parameters to evaluate the reproductive management programs are the days of open cows and the calving-conception interval. The former implies loss of income due to the fact that there are less lactation days and less calves per year. In normal cows, an open cow day consists of the physiological puerperium, that is to say the amount of days required for the first estrus to appear after calving, normally 10 days at least. This period, also called Voluntary Wait Period, cannot be substantially modified because it depends on physiological variables. The other components of these open cow days originate in estrus detection failures and conception failures and, in both cases, involve the addition of 21 days or more of the new estrus cycle to open cow days.
Therefore, a main reason to adopt a reproductive management program for dairy herds is the optimization of estrus detection and the improvement of conception rates.
Post-Calving Reproductive Management in Dairy Cows
During the post-calving period, dairy cows suffer an important change in their energy balance prior to the onset of the normal ovarian cycles. This negative energy balance is largely caused by the loss of energy resulting from lactation, larger than the energy that can be regained with food. This negative balance is associated to the hormonal plasma profiles determining a lower activity in the follicular dynamics and resulting in lack of estrus and ovulation. The reestablishment of LH pulsatile secretion after calving produces the restart of the normal follicular dynamics. The early beginning of the estrus cycles becomes a determining factor of an early conception. The moment of the first ovulation determines and limits the number of estrus cycles that are likely to occur before the first insemination, and the higher the number of estrus before the 60-day post-calving period, the higher the chance of conception at the first service (2.60 and 1.75 services per conception for cows of 0 and 4 estrus respectively before the 60-day post-calving period). The objective of the producers should be to fertilize the cow in the first or second insemination; otherwise, the number of open cow days would increase and the calving-conception period would be longer with the resulting production losses. An early presence of plasma progesterone prepares the uterus and the follicles for the cycles after the first ovulation to be complete and normal, therefore facilitating an early conception. It has been illustrated that low concentrations of progesterone (early post-calving) are associated to short anovulation cycles. Instead, high concentrations of progesterone are associated to normal and long cycles and normal ovulations. High progesterone concentrations (1 ng/ml) obtained through the application of intravaginal devices impregnated with progesterone result in this follicular replacement, inducing a normal differentiation at the level of the granulosa cells, determining the onset of the cycle and the development of a corpus luteus with normal luteal phases. The mechanism involves the increase in the frequency of LH pulses and of its action on the production of follicular estrogens, the development of LH receptors and the luteinization. In short, the beneficial effects of the treatments based on intravaginal devices after calving result in an anticipation of the normal cycles, therefore reducing the amount of open cow days and the calving-conception interval.
Neuroendocrine Control of the Estrus Cycle
The estrus cycle is regulated by a hormonal interaction ruled by the hypothalamus-hypophysis-ovary-uterus axis.
Hypothalamus
The hypothalamus forms the basis of the brain and its neurons produce the gonadotropin-releasing hormone or GnRH. This hormone spreads to the capillaries of the hypophysial portal system and from there to the cells of the adenohypophysis where it stimulates the synthesis and secretion of the hypophysial hormones, FSH and LH.
Hypophysis
It is formed by a frontal portion or adenohypophysis and a rear portion or neurohypophysis. The former produces several types of hormones, out of which FSH and LH play an essential role in the neuroendocrine control of the estrus cycle. The FSH hormone is responsible for the ovarian steroid genesis and the growth and maturation of the follicles, while the LH takes part in the ovarian steroid genesis process, the ovulation and the formation and maintenance of the corpus luteus. These hormones are secreted to the blood stream by means of pulses and are regulated by two systems: the tonic system and the cyclic system. The former produces the circulating basal level of hypophysial hormones which promote the development of the germinal and endocrine elements of the gonads. The cyclic system operates more sharply and becomes evident only during 12 to 24 hours in each of the reproductive cycles of the cow. The essential function of the cyclic mode is to cause the ovulation.
The neurohypophysis stores the oxytocin produced by the hypothalamus. This hormone takes part in several functions such the calving mechanism, the initiation of milk production and the transportation of the sperm. It is also presumably involved in the luteolysis.
Ovaries
The ovaries are exocrine glands (they release the ova) as well as endocrine glands (they secrete hormones). Among the hormones produced by the ovaries we can mention the estrogens, the progesterone and the inhibin. The estrogensxe2x80x94steroid hormonesxe2x80x94are produced by the ovarian follicle and act on different target organs such as the Fallopian Tubes, the uterus, the vagina, the vulva and the central nervous system, where they stimulate the estrus behavior, and the hypothalamus, where they produce a negative feedback on the tonic center and a positive feedback on the cyclic center.
The progesteronexe2x80x94steroid hormonexe2x80x94is produced by the corpus luteus because of the action of the LH. The effects of the progesterone are observed once the white tissue has been exposed for some time to estrogen stimulation. This preparation by the estrogens leads to a synergic effect.
This hormone prepares the uterus for the embryo implant and the gestation. At the hypothalamus level, it produces a negative feedback on the tonic center.
The inhibinxe2x80x94a protein hormonexe2x80x94is produced by the ovarian follicle (granulosa cells) and takes part in the FSH secretion regulation mechanism. It generates a negative feedback at the hypophysis level, resulting in a reduced FSH secretion.
Uterus
The uterus produces the prostaglandin F2xcex1 (PGF2xcex1) that takes part in the neuroendocrine regulation of the estrus cycle because of its luteolytic effect. It also takes part in the ovulation and calving mechanisms.
Phases of the Estrus Cycle
A description of the main events in the estrus cycle is included as follows.
The estrus cycle can be divided in three phases: 1) Follicular or luteal regression phase (proestrus), 2) periovulatory phase (estrus and metaestrus) and 3) luteal phase (diestrus).
Day 0 of the estrus cycle is the estrus day, that is to say the day on which the estrus can be visibly seen. However, from the physiological point of view, the description will begin with the destruction of the corpus luteus and end with the destruction of the corpus luteus of the next cycle.
1. Follicular or Luteal Regression Phase (Proestrus):
This 3-day period starts with the regression of the corpus luteus of the previous cycle and ends with the manifestation of the estrus. When the corpus luteus is destroyed, there is a fall in progesterone levels and, later on, a luteal tissue loss; in this process, the PGF2xcex1 of a uterine origin is the main luteolytic agent in domestic animals and most rodents.
As a result of the decline in progesterone levels, the negative feedback of this hormone at the hypothalamus level decreases as well and the pulsatile frequency of the gonadotrophic hormones (FSH and LH) starts to increase, stimulating the follicular growth with the development of a large follicle and the increase in estradiol levels.
When estrogens reach a certain level, the receptivity to the male becomes stimulated and the estrus cycle starts.
2. Periovulatory Phase (Estrus and Metaestrus)
This phase starts with the receptivity to the males (the cows allow both cows and bulls to mount them) and involves all changes allowing for the ovulation and the beginning of the corpus luteus formation.
During the estrus, lasting 18+/xe2x88x926 h, the cow shows restlessness and anxiety, bellows frequently and loses appetite. In the case of dairy cows, milk production becomes affected. The cows show a vaginal mucus discharge, whose smell appeals and excites the bull (presence of pheromones), vulva edema and an increase of the myometrial tone of the uterus, easily detected by transrectal palpation.
During this phase, the high concentrations of estrogens reach the stimulation threshold of the hypothalamic cyclic center, stimulating the hypothalamic neurons to produce the GnRH peak and consequently, the LH peak. As regards the FSH, its secretion decreases as a result of the negative feedback of the estrogens and the inhibin, except for the moment when the LH preovulatory peak occurs where a FSH peak can appear. Later, 4 to 12 hours after the LH wave, basal concentration and the FSH pulse width increase, and this process is related to the first wave of follicular growth.
From 12 to 24 hours after estrus beginning, the cow""s nervous system becomes refractory to estradiol and the psychic manifestations of the estrus come to halt.
The period immediately following the end of the estrus is called metaestrus (6 days). During this period, the ovulation of the cow occurs, unlike other species that ovulate during the estrus, giving rise to cell organization and the development of the corpus luteus. Ovulation occurs 28 to 32 hours after beginning of the estrus and is unleashed by the LH preovulatory peak. Ovulation is followed by a deep bleeding and the follicle is filled with blood and becomes a hemorrhagic body.
While the corpus luteus is formed (luteinization), a series of morphological and biochemical changes occur, allowing follicular cells to transform into luteal cells. These changes end on the seventh day with the formation of a functional corpus luteus.
3. Luteal Phase (Diestrus):
This phase is characterized by the predominance of the corpus luteus. The maintenance of the corpus luteus as well as the progesterone synthesis are related to the progesterotrohic and luteotrophic LH hormone.
Other hormones taking part in the progesterone synthesis are FSH and PGI2. The FSH hormone would apparently join to receptors located in the corpus luteus and would cause an increase in progesterone secretion. As regards PGI2, in addition to stimulating luteal cells to produce progesterone, it may increase the blood flow at the ovarian level, having a positive effect on the synthesis and secretion of progesterone.
If the ovum IS not fertilized, the corpus luteus remains functional until Day 15-20, after which regression starts in order to prepare for a new estrus cycle.
Follicular Dynamics of the Organisms
The growth and regression process of antral follicles leading to the development of a preovulatory follicle is known as follicular dynamics. There are between 1 and 4 follicular growth and development waves during the estrus cycle of the bovines and the preovulatory follicle derives from the last wave.
In order to describe the follicular dynamics of the bovines, it is necessary to define the concepts of recruitment, selection and dominance:
Recruitment: The process by which a cohort of follicles starts to mature in an environment with an adequate contribution of gonadotropins allowing for ovulation.
Selection: The process by which one of the follicles is selected, avoids the atresia and is likely to reach ovulation.
Dominance: The process by which the selected follicle dominates by exercising a inhibitory effect on the recruitment of a new cohort of follicles. This follicle becomes considerably bigger in size than the rest, is responsible for a higher estradiol secretion and acquires the capacity to continue developing in a hormonal environment that would be adverse for the rest of the follicles.
The cause of the regression of the dominant follicles of the first waves (1 out of 2 waves, and 2 out of 3 waves) seems to be the presence of low-frequency LH pulses due to the high levels of progesterone, which would result in a reduced androgen synthesis and consequently a reduced estradiol synthesis, giving rise to the beginning of the follicular atresia.
Resumption of the Activity After Calving
Follicular activity is normally absent in the first 10 days after calving, but starts to resume quickly after this period.
In well-fed dairy cows, the follicular wave activity is accompanied by follicular dominance. Therefore, it is common to find estrus onset and ovulation ten days after the calving. Beef cows follow a similar path. Resumption of the follicular waves has been observed ten days after calving. However, ovulation occurs later than in dairy cows (30.6 days in average).
In cows with an inadequate body condition and/or poorly fed, the follicular activity resumes also 10 days after calving in dairy cattle or about 30 days in beef cattle, but dominance can be absent for several weeks. In some primiparac, as many as 11 follicular waves were observed before a dominant follicle could finally ovulate.
Progesterone Role in the Estrus Cycle Control
Exposure to high progesterone levels followed by its decline (progesterone priming) seems to be pre-requisites for a normal differentiation of granulosa cells, a normal expression of the estrus and the post-ovulatory development of the corpus luteus with a normal luteal phase. This mechanism involves the effect produced by an increase in LH pulse frequency on the production of follicular estrogens, the development of LH receptors and the luteinization. The presence of a progesterone exogenous source imitates the inhibiting action of this hormone""s luteal levels on the LH pulsatile secretion, with the suppression of the dominant follicle growth and the resulting synchronic development of a new follicular development wave. The removal of this exogenous progesterone source allows for the increase in frequency and width of LH pulses and the growth of a dominant follicle, which will ovulate 48 to 72 hours later.
The use of intravaginal devices impregnated with progesterone is a common practice in animal production in order to synchronize the estrus in an organism, such as bovines (both dairy and beef), swine, equine and the like.
The use of a device results in a good synchrony of fertile estrus and becomes an essential tool for fixed-time artificial insemination patterns as well as for prefixed-time artificial insemination with a short period of estrus detection (36, 48 and 72 hours).
Artificial insemination costs, heavily influenced by the use of the products required for synchronization, have frequently restricted the application of this technology. Therefore, a significant effort was required to achieve an affordable cost level for the producers.
In this respect, the use of intravaginal devices, unlike other progestagens, offers the possibility of re-use and this results in a considerable cost reduction given the relative weight of progestagens on the remaining AI (Artificial Insemination) inputs.
For example, a profitable production of beef or milk often requires a maximum reproductive efficiency in today""s competitive market.
The factors contributing to this profitability are said to be: early services, high pregnancy rates, low prenatal losses, short lactation periods, high conception rates after early weanings and low frequency of anestrus animals.
Only a planned reproductive management can ensure good results in the abovementioned parameters and this requires an estrus control and/or synchronization system that can additionally improve the reproductive rates mentioned above.
Nowadays, the technology required to plan and control the estrus is available and affordable to the producers, who can get good results without modifying their operation management practices.
Several methods were used to control reproductive cycles, including products that interrupt the cycle by suppressing the ovarian activity (progestagens), products causing the regression of the corpus luteus (prostaglandins) or agents inducing and synchronizing the follicular development and the ovulation (combination of estrogens, progestagens and prostaglandins, PMSG, HSG, GNRH, and the like).
The use of estrogens, progestagens and prostaglandins provides the veterinarian with the necessary tools for a pharmacologically rational management of the estrus cycle, resulting in benefits such as the possibility of inseminating the animals on a fixed-time basis without estrus detection, recovery of animals with abnormal or absent estrus cycles and improvement of the overall fertility of the herd.
Earlier devices used to synchronize the estrus in cattle are typically known as CIDR (control of internal drug releasing) and were developed in New Zealand by the Ruakura Agricultural Research Centre and the Agricultural Division of the Carter Holt Harvey Plastic Products Group Ltd. Included within this range of devices is also the French PRID, developed by CEVA SANTE ANIMALE.
These devices consist of a nylon or coiled metal core (devoted to provide some rigidity to the device) covered with a Dow Corning 595 silicone elastomer containing 1.9 g (10% p/p) of progesterone.
The polymer used to make the CIDR device is a silicone of the vinyl-siloxane type (VMQ), reticulated using platinum as catalyst.
The PRID is a silicone elastomer coil with 1.55 g of evenly-spread progesterone and a gelatin capsule with 10 mg of estradiol benzoate.
The abovementioned intravaginal devices have generally the following characteristics:
a) The prior art devices have a progesterone dose over 1.5 g, typically 2 g, which increases considerably the cost of the inducing device;
b) The inductors of the prior art devices can be reused but in order to ensure a progesterone level over 1 ng/ml in blood plasma during 7 days (minimum level required to block the endogenous gonadotropins and allow for the effective synchronization of the dynamics of the follicle and the ovulation), both in use and reuse, additional injections of progesterone must be applied; in the case of the inductor containing an estradiol benzoate capsule (10 mg), the treatment is longer and takes at least 12 days.
c) The progesterone release curve (measured in plasma) in the first use vs. the length of time of the treatment with the prior art devices is significantly different from the one obtained during the prior art devices reuse.
d) The prior art devices are difficult to apply.
Further, various CIDR""s are manufactured from a liquid polymer that includes vinyl groups, since the polymer is reticulated with platinum. This type of curing, known as curing per addition, involves a first-order reaction occurring at a high speed and providing a high reticulation density. As a result of this curing process, the silicone rubber matrix obtained is highly rigid. Therefore, the progesterone released from the prior art devices is often characterized by a low spreading speed and this requires impregnation of the device with high doses of progesterone to achieve an acceptable drug release level.
Accordingly, it is an objective of the present invention is to provide an improved and new estrus-inducing devices and processes combining the following advantages and characteristics compared to prior art:
a) It is an object of various embodiments of the present invention, either alone or in combination with other objectives, to provide a device and/or process that utilizes a lower dose of progesterone than the prior art.
b) It is an object of various embodiments of the present invention, either alone or in combination with other objectives, to provide a device and process that allows progesterone absorption over 1 ng/ml in plasma during a 7-day treatment cycle both during repeated uses.
c) It is an object of various embodiments of the present invention, either alone or in combination with other objectives, to provide for a device and process whereby the progesterone release curves (measured as progesterone in plasma) versus the length of time of the 7-day treatment cycle are similar.
d) It is an object of various embodiments of the present invention, either alone or in combination with other objectives, to provide a device and process whereby an initial content of progesterone and a residual content of progesterone after use is comparable between repeated use(s) of the device.
e) It is an object of various embodiments of the present invention, either alone or in combination with other objectives, to provide a device and process whereby supplementation of the progesterone content with progesterone injections is not necessary through at least one repeated use, thereby resulting in less stress and in an equal shift in the follicular maturation wave as compared to organisms receiving a supplemental progesterone injection.
Embodiments of the present invention generally relate to intravaginal devices containing progesterone that can be used as an estrus inductor in an organism, such as bovine, swine, equine, and the like. Further, embodiments of the present invention generally relate to processes of manufacture and use of said devices.
Embodiments of the new devices of the present invention generally include the following characteristics, either alone or in combination:
a) An intravaginal anchoring structure. In various embodiments the anchoring structure comprises a cruciform and/or elastically deformable body, optionally with blind tubular branches defining a continuous inner duct connected to the outside through transversally-placed holes located along said tubular structure.
b) A nylon insert on said inner duct. In various embodiments, whose cross section together with the cross section of the inner duct define a free space along its surface.
c) A chamber located in the inner part of said cruciform body and, in various embodiments, connected to the outside by means of a hole.
d) In various embodiments, the anchoring structure consists of a phenyl-vinyl-silicone matrix reticulated with peroxide and homogeneously impregnated with about 1 g natural progesterone.
e) In a most preferred embodiment, but not meant as a limitation, the physical dimensions of the anchoring structure, free from substantial impregnation with progesterone, are as follows:
An embodiment of a device according to the present invention illustrates considerable differences as compared to prior art devices.
For example, a comparison of progesterone release curves with device insertion times illustrates that various prior art CIDR devices (with 1.9 g of progesterone) produce plasma progesterone concentrations that cannot be quantified until hours after the application of the device, in some cases, whereas embodiments of the present invention (with 1 g of progesterone) produce progesterone levels of 3 to 4 ng/ml in as little as 0.5 hours after device application, in most cases.
Various embodiments of a device of the present invention are made from a phenyl-vinyl-silicone reticulated with a peroxide curing technique. Various processes of these embodiments require only a second-order reaction, with slower curing times. Since the reaction speed is slower, the silicone reticulation level can be easily controlled, resulting in a mesh with enough flexibility and elasticity to facilitate progesterone spreading towards the surface of various embodiments of the present invention, while retaining adequate mechanical properties, such as rigidity.
As a result of improved flexibility and elasticity of peroxide-reticulated matrices, the progesterone spreading speed increases and allows for impregnation of the device with a smaller drug amount.
Another improvement found in various embodiments of the present invention is that the presence of holes connecting with the inner duct and the external surface allows progesterone to spread by following two alternative paths: (1) towards the external surface of the device; and, (2) towards the internal surface of the inner duct, from which the progesterone may spread along the inner duct towards communicating holes and through them to the outside or exterior of the device whereas the prior art CIDR devices only allow progesterone to spread towards the external surface.
A further improvement of various embodiments of the present invention is that at least one branch or at least one portion is larger than the respective portion or branch. By respective portion and/or branch is meant the branch and/or portion that extends from the intersection of the middle portion and the respective branch and/or portion. Such an arrangement allows a better anchor in the vaginal duct and/or more security in terms of any possible displacement of the device towards the outside during use/application. This improved rigidity in the side branches of the longitudinal shaft is accompanied by a higher flexibility in the opposing side branches. Further, the particular rigidity and flexibility of the present invention can be regulated through modification of the nylon core and/or curing processes.
Other embodiments of the present invention may also include at least one chamber inside or within the exterior of the device that is connected to the outside by means of a hole and/or passage which may be optionally sealable. A chamber of such embodiments may be utilized to contain supplementary additives to be used with the device, such as hormones, drugs, antiseptics, lubricants, and the like.
Further included within the scope of the present invention are processes related to estrus synchronization and processes for manufacture of various embodiments of the present invention.